The hardware needs an M chip and ability to offer better 4K video and audio to close the gap between blu-ray. Also the streaming service needs some major draw like Formula One, Rugby etc (NBA and NFL are too big imo)

Passthrough audio with bit perfect playback. To be completely honest, I think even Apple own Homepods speakers (specially the big ones, which support Dolby Atmos), would benefit from it, audio quality wise, when set up in home theater mode as Apple TV speakers, something that Apple is promoting very heavily these days…

It shouldn´t be the case, but I believe that Apple current implementation of a fixed 24 bit/48khz LPCM audio output for tvOS is detrimental to the overall sound quality. It tend to sound flat and low compared with devices that support bitstream/passthrough, and I dont know why.